Many military aircraft and other vehicles include on their outer structures radiofrequency signal absorptive coatings. These coatings provide to the vehicle the attractive feature of being less detectable by active radar systems that detect the presence of the vehicle by sending a radiofrequency signal in the direction of the vehicle and detecting the signal's reflection by the vehicle's outer reflective surface. The radiofrequency signal absorptive coatings deter detection by essentially forming an attenuative envelope that surrounds and hides the vehicle. These coatings are typically thin, on the order of approximately 0.015 inches to 0.040 inches thick, and often contain 40 to 45 volume percent carbonyl iron powder (CIP). During maintenance or in the event of damage to the coating, the envelope that the absorptive coating forms can have an opening. Such an opening exposes the underlying reflective surface of the vehicle. To restore the integrity of the absorptive coating, it is necessary to seal the opening by reworking and repairing the radiofrequency signal absorptive coating.
Rework and repair of attenuative coatings in the field has been addressed in several ways for the various types of coatings that military aircraft and other vehicles presently use. Generally, these materials consist of multi-component materials that are sprayed or bonded to the affected region. These materials exhibit significant reliability, maintainability, and sustainability limitations. One problem is that there are often significant cure times that must pass before placing the affected vehicle back in service. For example, existing repair compounds use epoxies or urethanes that require over two hours to cure. In a tactical situation, however, it is often not feasible to prohibit the aircraft from flying following a repair for more than two hours. As a result, openings in these coatings will go unrepaired on aircraft that cannot land and wait the necessary time for the epoxy or urethane to cure. Failing to repair the coating subjects the aircraft to detection and makes it more vulnerable. The two hour cure time of known repair techniques, therefore, can significantly affect the operational capability of the vehicle itself.
Because of the above reasons, a key factor in governing the ultimate utility of an absorptive coating repair and rework system is the cure time of the repair compound. These factors, however, must be balanced with the pursuit of a material that field personnel can easily apply to restore the coating to its original performance level. Known repair compounds, for example, are messy, toxic, and often require a substantial degree of finishing or sanding to restore the absorptive coating to its original effectiveness. A further limitation of existing repair compounds is that they do not easily form into or fill gaps or small openings in the associated vehicle surface. If the system is not easy to apply, field personnel will in many cases elect not to use it rather than suffer the unacceptable down time and frustration that working with it presents. This also degrades the overall performance of the absorptive coating.
Consequently, there is a need for a method and system for repairing and reworking attenuative coatings on vehicles such as a military aircraft.
There is a further need for a system for sealing a radiofrequency signal absorbing coating that is easy to apply with a minimal degree of finishing after application.
There is also a need for a method and system for sealing attenuative coating that possess attractive characteristics such as desirable gap filling properties, high and low temperature performance, and environmental suitability.